Field of the Invention
The present invention relates to wireless communications, and more particularly, to a device-to-device (D2D) operation method performed by a terminal in a wireless communication system and a terminal using the method.
Related Art
In an International Telecommunication Union Radio communication sector (ITU-R), a standardization of International Mobile Telecommunication (IMT)-Advanced being a next mobile communication system after a third generation has been performed. The IMT-Advanced is aimed at supporting an Internet Protocol (IP) based multi-media service with a data transmission rate of 1 Gbps in a stop and low speed moving state and a data transmission rate of 1 Gbps in a high speed moving state.
A 3rd Generation Partnership Project (3GPP) is preparing LTE-Advanced (LTE-A) being an improved one of Long Term Evolution (LTE) based on an OFDMA (Orthogonal Frequency Division Multiple Access)/SC-FDMA (Single Carrier-Frequency Division Multiple Access) transmission scheme as a system standard satisfying requirements of IMT-Advanced. The LTE-A is one important candidate for IMT-Advanced.
In recent years, there is growing interest in a Device-to-Device (D2D) technology performing direct communication between devices. In particular, the D2D is attracting attention as a communication technology for a public safety network. A commercial communication network has been rapidly changed to the LTE but a current public safety network is based on a 2G technology in a collision problem and a cost side with an existing communication standard. Request for the technology clearance and an improved service induces an effort to improve the public safety network.
The public safety network has high service requirements (reliability and security) as compared with a commercial communication network. In particular, when coverage of cellular communication is insufficient or is not used, there is a need for direct signal transmission/reception between devices, that is, a D2D operation.
The D2D operation may be signal transmission/reception between adjacent devices to have various advantages. For example, a D2D terminal may perform data communication with a high transmission rate and low delay. Further, the D2D operation may distribute traffic converged in a base station. If the D2D terminal serves as a relay, the D2D terminal may serve to extend coverage of a base station.
Meanwhile, a terminal is required to perform a D2D operation with another terminal even when being located side cell coverage, because the D2D operation is mainly for public safety/disastrous situations. To this end, the terminal may be assigned a resource for a D2D operation in advance. Such a resource is referred to as a preconfigured resource. The terminal may perform D2D transmission in mode 2 using the preconfigured resource.
Mode 2 refers to a mode in which a terminal autonomously selects a specific resource in a defined resource pool and transmits a D2D signal through the selected resource. In mode-2 D2D signal transmission, a terminal may select a specific resource among the predetermined resources or may select a specific resource in a resource pool configured by a network. On the contrary, mode 1 refers to a mode in which a D2D signal is transmitted using a resource scheduled by a network.
Meanwhile, when a terminal, which is located outside cell coverage, enters the cell coverage, the terminal may acquire a mode-2 transmission resource from system information provided by a base station of a cell. However, if the system information simply indicates the mode-2 transmission resource only, the terminal may not know whether the mode-2 transmission resource is applied in a radio resource control (RRC) idle state or is applied only in an RRC connected state.
Further, although the network does not configure or reports the mode-2 transmission resource to the terminal, the network may need to control whether to allow the terminal to use the preconfigured resource in the cell coverage.